The rotating torque of an induction motor is produced by an interaction between a rotating magnetic field generated by its stator winding and an induced current flowing through its rotor winding. The rotor and stator windings are represented by a motor equivalent circuit, in which the motor parameters of primary and secondary resistances and leakage inductance determine the voltage-current characteristics of the induction motor.
Methods for controlling a motor described in Patent Documents 1 to 3 use motor parameters set in a controller to control the output currents and voltages of an inverter such that the actual velocity follows the rotational velocity command value ωr*. Such controls can obtain a good controllability only when actual values of the parameters such as the primary resistance in the motor equivalent circuit match the motor parameters used for the control. Patent Documents 4 discloses a technique which determines the motor parameters and set control parameters in the controller based on the determined results. This parameter determining method determines the primary resistance and leakage inductance based on the deviation of an actual d-axis current from a d-axis current command value. In this method, the primary resistance is determined under a specific operating condition in which at least one of the frequency command value and q-axis current is less than a predetermined value, while the leakage inductance is determined under a specific operating condition in which the frequency command value and q-axis current are both no less than a predetermined value.
[Patent Document 1] Japanese Patent Laid-open No. Hei 6 (1994)-105580
[Patent Document 2] Japanese Patent Laid-open No. Hei 6 (1994)-284771
[Patent Document 3] Japanese Patent Laid-open No. Hei 8 (1996)-317698
[Patent Document 4] Japanese Patent Laid-open No. Hei 9 (1997)-191699